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#3389966 - 06/05/14 04:44 PM Question for Subaru manual transmission owners
buster Offline


Registered: 11/16/02
Posts: 30301
Loc: NJ
I've read that the viscous coupling/center differential usually fail around 150,000 miles. Are these common failures? I can't get a good answer from the Forester forum (yet).

And what exactly causes them to fail other than mismatched tires? Does the fluid shear to the point that it can't transfer power as effectively?
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#3389972 - 06/05/14 04:49 PM Re: Question for Subaru owners [Re: buster]
147_Grain Offline


Registered: 03/11/13
Posts: 1945
Loc: USA
IF you change out the center differential fluid on a regular basis, say every 30,000 like I do, then there should be no problems. 4-cylinder models have a viscous coupling differential that is easy to drain and fill.

My 6-cylinder Outback has the central viscous coupling inside the 5-speed (5EAT) auto transmission, which I service with 4 quarts of Subaru ATF-HP each spring. Cheap insurance for both the tranny and center differential.

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#3389979 - 06/05/14 04:58 PM Re: Question for Subaru owners [Re: buster]
Bandito440 Offline


Registered: 02/13/12
Posts: 3735
Loc: NYS
That's an issue I haven't heard of. I plan on swapping out the fluid in the MTF and rear diff every 30k or so. I did an early swap with plain 75w-90 conventional Valvoline, and that's what I'll be using from now on.
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#3389991 - 06/05/14 05:16 PM Re: Question for Subaru owners [Re: 147_Grain]
Rand Offline


Registered: 08/20/03
Posts: 11904
Loc: NE,Ohio
A few problems with this.

There is no vicious coupling on AT models.. instead there is a "Electronically controlled hydraulic multi-plate transfer clutch"

Most Subaru's with MT's have the vicious coupling system which is sealed so changing the fluid doesnt prolong its life either... although I'm not saying dont change the fluid.. changing it will not have much effect on the sealed vicious coupling.

Originally Posted By: 147_Grain
IF you change out the center differential fluid on a regular basis, say every 30,000 like I do, then there should be no problems. 4-cylinder models have a viscous coupling differential that is easy to drain and fill.

My 6-cylinder Outback has the central viscous coupling inside the 5-speed (5EAT) auto transmission, which I service with 4 quarts of Subaru ATF-HP each spring. Cheap insurance for both the tranny and center differential.
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#3390005 - 06/05/14 05:38 PM Re: Question for Subaru owners [Re: Rand]
buster Offline


Registered: 11/16/02
Posts: 30301
Loc: NJ
Originally Posted By: Rand
A few problems with this.

There is no vicious coupling on AT models.. instead there is a "Electronically controlled hydraulic multi-plate transfer clutch"

Most Subaru's with MT's have the vicious coupling system which is sealed so changing the fluid doesnt prolong its life either... although I'm not saying dont change the fluid.. changing it will not have much effect on the sealed vicious coupling.

Originally Posted By: 147_Grain
IF you change out the center differential fluid on a regular basis, say every 30,000 like I do, then there should be no problems. 4-cylinder models have a viscous coupling differential that is easy to drain and fill.

My 6-cylinder Outback has the central viscous coupling inside the 5-speed (5EAT) auto transmission, which I service with 4 quarts of Subaru ATF-HP each spring. Cheap insurance for both the tranny and center differential.


Right. It's a sealed unit. You can't change the fluid on a VC. The MTF is different.

When the viscous coupling fails, the AWD is essentially gone.
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#3390048 - 06/05/14 06:46 PM Re: Question for Subaru owners [Re: buster]
LoneRanger Offline


Registered: 07/02/07
Posts: 3253
Loc: Midwest USA
I've never heard of any failures. Mine has the VCD, and it works super great! With the Nokian WRG2 tires I have on it the thing doesn't know how to spin in snow, it just claws with all four paws and goes. The system also worked great in the sand dunes here:

http://www.thinkdunes.com/sand-dunes-7/

...once I deflated to about 12 psi each tire.
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'09 Subaru Forester ...................(QSED DEXOS1 5W30)
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#3390103 - 06/05/14 08:01 PM Re: Question for Subaru owners [Re: buster]
skyactiv Offline


Registered: 03/02/13
Posts: 3136
Loc: The Midwest
The center diff can be replaced with the transmission still in the car on some Subarus. Not sure which ones.
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#3390110 - 06/05/14 08:06 PM Re: Question for Subaru owners [Re: LoneRanger]
buster Offline


Registered: 11/16/02
Posts: 30301
Loc: NJ
Originally Posted By: LoneRanger
I've never heard of any failures. Mine has the VCD, and it works super great! With the Nokian WRG2 tires I have on it the thing doesn't know how to spin in snow, it just claws with all four paws and goes. The system also worked great in the sand dunes here:

http://www.thinkdunes.com/sand-dunes-7/

...once I deflated to about 12 psi each tire.


The automatics use the MPT though and not a VC. They are great in sand/snow. There really isn't a better vehicle for bad weather.
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#3390116 - 06/05/14 08:11 PM Re: Question for Subaru owners [Re: LoneRanger]
Rand Offline


Registered: 08/20/03
Posts: 11904
Loc: NE,Ohio
Is your subaru auto or manual? If its manual it has a vicious coupling

If its auto it has MPT otherwise known as an "Electronically controlled hydraulic Multi-Plate Transfer clutch"

Originally Posted By: LoneRanger
I've never heard of any failures. Mine has the VCD, and it works super great! With the Nokian WRG2 tires I have on it the thing doesn't know how to spin in snow, it just claws with all four paws and goes. The system also worked great in the sand dunes here:

http://www.thinkdunes.com/sand-dunes-7/

...once I deflated to about 12 psi each tire.


Edited by Rand (06/05/14 08:12 PM)
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#3390117 - 06/05/14 08:11 PM Re: Question for Subaru owners [Re: buster]
gathermewool Online   content


Registered: 01/09/09
Posts: 5200
Loc: New England
I haven't researched this, but I'll hazard a guess at the most likely cause. It requires a viscous fluid to transfer torque, so the viscous coupling will most likely degrade or become inoperable if enough or all of the fluid leaks out due to a seal failure, as they tend to do with age.

If I had to guess further, abuse in the form of rally-cross and off-roading or high slip-rates while hooning on snow days will severely shorten its life, while typical use will slowly wear away at the unit, just as with a rear differential.

The rear differential in my previous Subaru didn't have any leaks after >200k miles, so I can't see why a VC center couldn't last just as long if used for its intended purpose - transfer torque between the front and rear, in a controlled, steady manner, which also coincides with the safest approach to driving in bad weather...go figure.
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#3390123 - 06/05/14 08:18 PM Re: Question for Subaru owners [Re: buster]
Clevy Offline


Registered: 11/11/10
Posts: 9783
Loc: Saskatoon canada
Originally Posted By: buster
Originally Posted By: LoneRanger
I've never heard of any failures. Mine has the VCD, and it works super great! With the Nokian WRG2 tires I have on it the thing doesn't know how to spin in snow, it just claws with all four paws and goes. The system also worked great in the sand dunes here:

http://www.thinkdunes.com/sand-dunes-7/

...once I deflated to about 12 psi each tire.


The automatics use the MPT though and not a VC. They are great in sand/snow. There really isn't a better vehicle for bad weather.


I'm really getting to see the benefits of awd. My c3 is awd. I gotta admit I like not having to physically shift into 4wd and I've had this truck on sites so greasy my forklift has a tough time getting through.
The c3 will engage the front tire as soon as it senses the rear tires slip and the tire speed is different from front to rear.
If will go through any common muddy or slick road surfaces.
I'm buying new 4wd trucks shortly and I'm going to be sad handing the keys over to my girl.
I'm sure the gmc awd system isn't as sophisticated as Subaru however thus far I'm pretty happy.
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#3391496 - 06/07/14 02:26 PM Re: Question for Subaru owners [Re: buster]
buster Offline


Registered: 11/16/02
Posts: 30301
Loc: NJ
I ended up talking to a very knowledgeable Subaru tech and he said they can last 200k + depending on the how it was used. Subaru Powa.
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#3391563 - 06/07/14 04:32 PM Re: Question for Subaru owners [Re: buster]
Kiwi_ME Offline


Registered: 10/24/08
Posts: 1019
Loc: New Zealand
Originally Posted By: buster


Right. It's a sealed unit. You can't change the fluid on a VC. The MTF is different.

When the viscous coupling fails, the AWD is essentially gone.


I'm not sure that's technically correct, depending what you mean by "failure." The manual Subaru has a center diff which will work even if the viscous "LSD" feature is diminished. It's actually more like full-time 4WD.

The automatics with their multi-plate clutch are a totally different AWD concept which is similar to just about every FWD-based on-demand AWD vehicle with electronic control, bringing in the rear axle only when useful. Subaru seems to have done a better job however and they are highly-regarded.

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#3392099 - 06/08/14 10:49 AM Re: Question for Subaru owners [Re: buster]
JTK Offline


Registered: 08/14/03
Posts: 9815
Loc: Buffalo, NY
So the viscous coupling internal to a current 5 or 6spd Subaru manual trans is sealed with it's own fluid? I had no idea if so.

I know the 5spd in my new XV looks about as easy to do an oil change on as the engine. It has a drain plug and a top fill w/ dipstick. I was under the impression that the trans full of 75w90 (3.7quarts IIRC), lubed the whole system; Gearbox, diff and visc cplg.


Edited by JTK (06/08/14 10:50 AM)
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2016 Subaru Forester 2.5, CVT. 2016 Nissan Quest SV (Babe magnet IV)

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#3392235 - 06/08/14 02:14 PM Re: Question for Subaru owners [Re: JTK]
Kiwi_ME Offline


Registered: 10/24/08
Posts: 1019
Loc: New Zealand
Well, by definition the viscous coupling must have it's own fluid. A fluid that gets thicker when it's hot.

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#3392298 - 06/08/14 03:41 PM Re: Question for Subaru owners [Re: Kiwi_ME]
JTK Offline


Registered: 08/14/03
Posts: 9815
Loc: Buffalo, NY
I get that somewhat.

Just curious because in the ~3yrs I've been active on Subaru boards I've never heard this talked about.

Still cant figure out how it's fluid is kept separate with the 75w90 gear oil.
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2016 Subaru Forester 2.5, CVT. 2016 Nissan Quest SV (Babe magnet IV)

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#3392314 - 06/08/14 04:01 PM Re: Question for Subaru owners [Re: JTK]
Rand Offline


Registered: 08/20/03
Posts: 11904
Loc: NE,Ohio


10 is center diff
11 is VC
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#3392419 - 06/08/14 06:41 PM Re: Question for Subaru owners [Re: Kiwi_ME]
Rand Offline


Registered: 08/20/03
Posts: 11904
Loc: NE,Ohio
+1 this post is correct.

on the auto if the MPT fails you end up with FWD basically.

on the manual if the VC fails you still have 4wd..just can get 1 wheel peel on any of the 4 wheels.

Originally Posted By: Kiwi_ME
Originally Posted By: buster


Right. It's a sealed unit. You can't change the fluid on a VC. The MTF is different.

When the viscous coupling fails, the AWD is essentially gone.


I'm not sure that's technically correct, depending what you mean by "failure." The manual Subaru has a center diff which will work even if the viscous "LSD" feature is diminished. It's actually more like full-time 4WD.

The automatics with their multi-plate clutch are a totally different AWD concept which is similar to just about every FWD-based on-demand AWD vehicle with electronic control, bringing in the rear axle only when useful. Subaru seems to have done a better job however and they are highly-regarded.
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2017 Jeep Cherokee Trailhawk V6

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#3393086 - 06/09/14 02:27 PM Re: Question for Subaru owners [Re: buster]
buster Offline


Registered: 11/16/02
Posts: 30301
Loc: NJ
Thank you, that is correct. However, when the VC goes, the torque transfer is gone. For the MT, it's 50/50 with up to 80/20 20/80 transfer with a properly working VC.
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#3393136 - 06/09/14 03:26 PM Re: Question for Subaru owners [Re: buster]
Kiwi_ME Offline


Registered: 10/24/08
Posts: 1019
Loc: New Zealand
Well, obviously with a component failure something has to change but it's not like it's going to leave you stranded!

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#3393310 - 06/09/14 06:52 PM Re: Question for Subaru owners [Re: buster]
LoneRanger Offline


Registered: 07/02/07
Posts: 3253
Loc: Midwest USA
Someone asked if mine was Manual or Automatic. It's a manual. It's really fun to drive. Using engine braking coming into the entry to a curve then powering through the apex really works well with the this style of AWD Subaru uses in their manual trans. The Nokian WRG2's were a tad squirmy in curves when new but after being scrubbed-in, they handle surprisingly well for such an aggressively siped winter style tread.

The only thing that is a little not perfect is 1st gear ratio is pretty short. I'm shifting to 2nd by the other side of the intersection. But then the short 1st helps for soft road / off road. Although a genuine low range would be best. I think in the Australian market Subaru was offering a low range.
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'09 Subaru Forester ...................(QSED DEXOS1 5W30)
'16 Moto Guzzi Stelvio 1200 .....(Factory fill)

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#3394397 - 06/10/14 09:52 PM Re: Question for Subaru owners [Re: buster]
bulwnkl Offline


Registered: 02/09/05
Posts: 1670
Loc: Arizona
Go have a look around at the Ultimate Subaru Message Board. It's a _much_ more helpful place than many of the model-specific boards, because the guys there tend to be more mechanical types, and interesting-project-types, and so forth. There are PLENTY of threads on failed power transfer clutch packs in most of the A/T Subies, and even a few about the potential for the LSD packs in the M/Ts failing.

There isn't any _good_ reason for the LSD pack in one of the M/Ts to fail before the tranny itself. You'd really have to be beating on it, or rallying it, or something of that sort, IMO.
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#3394686 - 06/11/14 09:43 AM Re: Question for Subaru owners [Re: buster]
buster Offline


Registered: 11/16/02
Posts: 30301
Loc: NJ
Thanks bulwnkl!
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